Field of the Invention
The present invention relates to a multimode resonator using the transmission lines and proposes to provide any of the techniques whereby the higher-order mode resonance frequencies can be varied by changing the structure of the resonator mentioned above. The present invention also relates to any of the methods for providing the structures of RFID tags and a tag system whereby the code information can be assigned to the structure of the multimode resonator and each of the codes is made to correspond to each of the combinations of the higher-order mode resonance frequencies that are produced in response to each corresponding structure of the resonator so that the code can be associated with each corresponding combination of the higher-order mode resonance frequencies.
Description of the Relevant Art
Bar codes are used widely in the inventory management, the goods distribution management and other similar managements, and may have some distinguished features because ID tags can be printed out and are very inexpensive. The bar codes have several problems associated with the tag reliability because it is poor, however. Specifically, the tag reliability problems may includes the problems in that the tags cannot be kept confidential or secret (that is, they are completely exposed), the tags are easy to be recognized incorrectly if when they are contaminated or dirty, and are easy to be exposed to any act of altering the tags improperly. Other problems may include the problems in that the area over which the tags can be read is restricted and the presence of some obstacles or obstructions, if any, might prevent the tags from being read correctly.
The conventional version of the RFID (Radio Frequency Identification) which is implemented on any semiconductor chip has been used more widely and is primarily intended to eliminate the problems mentioned above. In this respect, the conventional RFID has some distinguished features in that the tags can be both read and written easily.
It should be noted, however, that the tags that have been composed of the semiconductor chips implemented on printed circuit board may become high costly and have several problems in that the tags cannot be used under the high temperature environment that may cause the semiconductor chip to operated improperly or under the environment in which the tags are exposed to the strong radiation rays.
The present invention concerns the chipless RFID tags which are provided to replace the conventional bar code function.
In accordance with one embodiment of the present invention, the chipless RFID tags are provided so that they can essentially take advantage of the resonance characteristics of the transmission line resonator. This allows the internal circuit not to be exposed to the outside, that is, not to be seen from the outside. In this respect, the tag information can be kept more confidential or secret and the resistance to any act of altering the tags can become much stronger than that for the conventional bar codes. As other features, the tag information can be read out regardless of the presence of any type of obstacles or obstructions such as paper, cloth, wood and the like other than metal and the tags can be embedded in any type of objects such as the living body when they are miniaturized so that they can operate with the millimeter wave band. In addition, those tags can be implemented on the passive circuit, and they can be operated in the wider temperature range or under the environment in which the tags may be exposed to the radiation rays without being operated improperly.
In accordance with the present invention, the RFID tags are not so cost competitive as the bar code tags and the RFID does not require so many functions as the conventional version of the RFID that was implemented on the semiconductor chip. The tags can be used in those applications or environments in which the tags cannot be used or are difficult to be used.
There are various technologies for the chipless RFID that are disclosed in the documents cited below and have been used in the practical applications.